Inverting/non-inverting Op-amp Inputs !!!help!!!

IIR · 7th May 2002, 02:16 AM

COnsider this circuit. A typical op-amp like conifguration. Could someone PLEASE explain to be which input is the inverting input and which is the non inverting input based upon which leg you take from the diff-amp???

I have seen circuit examples but I want an explanation. Thanks in advance!

IIR · 7th May 2002, 02:18 AM

Another question. Where is the best place to put DC offset trim? is R5 correct for this?

Thanks again in advance

djk · 7th May 2002, 10:55 AM

Yes, R5 will trim the DC. With the input on the base, the collector output is inverted. Thus, if the base of Q2 is hooked to the collector of Q3, the output of Q2 is non-inverting when Q3 is the input. If Q4 was the input and Q2 hooked to its collector then the output of Q2 would still be non-inverting. If Q4 was the input and Q2 was hooked to Q3 the amp would be inverting. If Q3 was the input and Q4 hooked to Q2 the output would be inverting. For $6 AudioXpress will sell the Pass A40 circuit board which will allow you to experiment with this circuit. Or build an amp. I built a 250W/ch amp with a pair of these.

sonnya · 7th May 2002, 11:17 AM

Why have you placed r1 and r2 on the collector of Q1 and Q2?

Sonny

Nelson Pass · 7th May 2002, 10:17 PM

Probably the take off point for driving Q23 should be
below R1 or R2.

The non-inverting input will be the one whose collector
drives the base of Q23

sonnya · 7th May 2002, 10:37 PM

Nelson pass wrote : "The non-inverting input will be the one whose collector drives the base of Q23"

Listen to him.

For r1 and r2, put them somewhere more usefull .. On the emitter of Q1 and Q2 to balance the currentmirror.

Sonny

peranders · 7th May 2002, 10:49 PM

IIR, if you check my monster phono amp or my monster headphone amp you can get some idea of differential stages and design of a discrete opamp.

http://home5.swipnet.se/~w-50719/hifi/qsxm2/index.html

http://home5.swipnet.se/~w-50719/hifi/qrv01/index.html

IIR · 8th May 2002, 02:48 AM

If I understand correctly this circuit is correct:

The current mirror is what threw me off.

IIR · 8th May 2002, 02:50 AM

BTW:

What is the website for that audio express website???

Thanks

Jocko Homo · 8th May 2002, 03:06 AM

You might want to increase the value of R6. I hope this is not supposed to be a power amplifier.

Jocko

7th May 2002, 02:18 AM	#2
IIR diyAudio Member Join Date: Apr 2002	Addendum Another question. Where is the best place to put DC offset trim? is R5 correct for this? Thanks again in advance

7th May 2002, 10:49 PM	#7
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Typical design IIR, if you check my monster phono amp or my monster headphone amp you can get some idea of differential stages and design of a discrete opamp. http://home5.swipnet.se/~w-50719/hifi/qsxm2/index.html http://home5.swipnet.se/~w-50719/hifi/qrv01/index.html __________________ /Per-Anders (my first name) or P-A as my friends call me Tube Buffered Gainclone in work \|Thread

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7th May 2002, 10:55 AM	#3
djk diyAudio Member Join Date: Feb 2001 Location: USA	Yes, R5 will trim the DC. With the input on the base, the collector output is inverted. Thus, if the base of Q2 is hooked to the collector of Q3, the output of Q2 is non-inverting when Q3 is the input. If Q4 was the input and Q2 hooked to its collector then the output of Q2 would still be non-inverting. If Q4 was the input and Q2 was hooked to Q3 the amp would be inverting. If Q3 was the input and Q4 hooked to Q2 the output would be inverting. For $6 AudioXpress will sell the Pass A40 circuit board which will allow you to experiment with this circuit. Or build an amp. I built a 250W/ch amp with a pair of these.

7th May 2002, 11:17 AM	#4
sonnya diyAudio Member Join Date: Oct 2001 Location: Denmark	Why have you placed r1 and r2 on the collector of Q1 and Q2? Sonny

7th May 2002, 10:17 PM	#5
Nelson Pass The one and only Join Date: Mar 2001	Probably the take off point for driving Q23 should be below R1 or R2. The non-inverting input will be the one whose collector drives the base of Q23

7th May 2002, 10:37 PM	#6
sonnya diyAudio Member Join Date: Oct 2001 Location: Denmark	Nelson pass wrote : "The non-inverting input will be the one whose collector drives the base of Q23" Listen to him. For r1 and r2, put them somewhere more usefull .. On the emitter of Q1 and Q2 to balance the currentmirror. Sonny

8th May 2002, 02:50 AM	#9
IIR diyAudio Member Join Date: Apr 2002	BTW: What is the website for that audio express website??? Thanks

8th May 2002, 03:06 AM	#10
Jocko Homo Banned Join Date: Feb 2002 Location: As far from the NOSsers as possible	You might want to increase the value of R6. I hope this is not supposed to be a power amplifier. Jocko